This invention relates to a frame construction and more particularly to a frame construction suitable for use in power mining equipment and the like such as drag lines, stripping shovels, loading shovels, cranes, and the like. In particular, this invention contemplates a novel construction for mounting the roller circle system between the rotating portion and the base portion of the power mining device so as to minimize the adverse effects on roller bearings of hard spots caused by the intersection of bulkheads or ribs which strengthen the rotating frame and the base.
Generally speaking, heavy duty power machines in the prior art have consisted of a lower frame or base adapted to be seated on the ground, a bearing roller circle mounted on the lower frame, an upper rotatable frame mounted on the roller circle for swing movement relative to the lower frame or base, a boom mounted on the front end of the upper frame supporting a drag line bucket, shovel or the like, a gantry and possible a mast mounted on the upper frame for supporting the boom by means of pendants and associated machinery mounted on the upper frame for operating the drag line bucket, shovel or the like, swinging the upper frame and propelling the machine.
Traditionally, both the upper frame and the lower frame or base have consisted of an outer wall, a grid structure disposed within the outer wall including a plurality of longitudinally and transversely disposed frame members or bulkheads welded together and to the outer wall, and upper and lower plates welded to the grid structure. A plurality of arcuate, vertical ribs rigidly interconnect the transverse bulkheads and longitudinal ribs and are disposed concentrically relative to the center journal about which the upper frame rotates to form a reinforced circular path or pad for supporting the upper or lower bearing rail of the roller bearing assembly.
It is well known that the eccentric load imposed by the boom or a combination of a boom and a dipper handle and the limited arc of travel of the upper frame of these machines during normal operation, results in the application of non-uniform and highly concentrated loads on small segments of the bearing roller circles of such machines. Unless certain measures are taken to alleviate such highly concentrated loads and the high stresses developed by such loads, the rails and/or roller bearings begin to deteriorate and they eventually fail. The failure of rails and roller bearings of large machines is a costly matter. Where such failure occurs, the machine must be taken out of service thus adversely affecting its productivity and the rails and/or roller bearings must be replaced which are costly in materials and labor.
In the prior art, several approaches have been taken to reduce rail and roller failure and thus prolong the service life of the roller bearings. Rails and roller bearings have been redesigned. The metallurgy of rails and roller bearings has been improved. More recently it has been proposed to install a cushioning material such as rubber, neopreme or polyurethane between the upper rail and the upper frame and/or between the lower rail and the lower frame principally for the purpose of more uniformly distributing load imposed on the roller circle over a greater arc thereby including a greater number of rail segments and roller bearings.
However, still another problem exists in the construction of the upper and lower frames which causes a deleterious effect upon the roller bearings which has not been solved by the prior art. In the construction of the grid structures forming the upper frame and the base structures, the intersection of the transversely and longitudinally disposed bulkheads or ribs as well as the intersection of the arcuate vertical ribs forming the reinforced circular path for mounting the upper and lower bearing rails create "hard spots" in the structure and thus the grid is more rigid or stiff at these points than elsewhere.
Front end loads and the weight of the machine, when applied at various points on the rotating frame structure, are transferred to ground supports under the base or lower frame through the bearing rails and the roller circle bearing rollers. Bearing roller load distribution and maximum bearing roller load carried by any bearing roller depend upon the stiffness of the rotating frame and the base frame structures in the roller path. Thus, the rotating frame, the base frame, the bearing roller circle and the ground support system can be viewed as four springs of different spring rate or stiffness connected in series. The combined stiffness of the system at any point in the bearing roller path determines the load carried by the roller bearing at that point. The spring rate or stiffness of the rotating frame along the roller circle support varies and is comparatively stiffer at an intersection of one or more of the bulkheads with the annular roller support bulkhead.
Thus, peak roller loads of two and one-half to three times the magnitude of normal roller load result when the bearing roller is positioned between a "hard spot" on the rotating frame and the base frame. Fatigue life of the bearing rails, the rollers, and the rib intersections under the bearing rails in the base frame as well as in rotating frame can be improved by softening some of the "hard spots" in the rotating frame and/or the base frame where the roller circle support bulkheads or ribs intersects one or more of the transverse and longitudinal bulkheads or ribs. By sandwiching a brass plate or a plate of any other metal softer than steel between the bearing rail and upper rotating frame or base in the hard spot areas will result in a reduction of stiffness in those areas. Reduced stiffness of the rotating frame structure or base frame in the hard spot areas will result in a more uniform stiffness in the roller path and thus reduce peak loads by disbursing peak loads on adjacent rollers.
Thus, it is a principal object of the present invention to reduce the stiffness of the rotating frame structure or the base frame in hard spot areas thereby reducing bearing failure and frame structure failure in those areas.
It is still another object of the present invention to sandwich a material softer than steel such as brass between the bearing rails and the frame structure in hard spot areas to obtain the resulting reduction of stiffness in those hard spot areas.
It is also an object of the present invention to form a recess in the rail segments that are positioned over selected bulkhead intersections causing the hard spots and inserting a brass plate in said recess and rigidly attached to the rail segment whereby a reduced relative stiffness between the hard spots and the bearing rollers occur.
It is yet another object of the present invention to form a recess in the underside of the bottom plate of the rotating frame over selected bulkhead intersections forming the hard spots and attaching a plate of softer material such as brass in the recess between the rotating frame and the upper rail segments whereby the deleterious effects of the hard spots on the bearings are minimized by an overall reduction in stiffness.
It is a further object of the present invention to form a recess in the upper surface of the base upper plate over selected ones of the bulkhead intersections forming the hard spots and attaching a plate of metal softer than steel in the recess between the base and the lower rail segments whereby the deleterious effects of hard spots on the bearings are minimized by an overall reduction in stiffness.